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ERF(P)				    POSIX Programmer's Manual				   ERF(P)

NAME
       erf, erff, erfl - error functions

SYNOPSIS
       #include <math.h>

       double erf(double x);
       float erff(float x);
       long double erfl(long double x);

DESCRIPTION
       These functions shall compute the error function of their argument x, defined as:

       An  application	wishing  to  check for error situations should set errno to zero and call
       feclearexcept(FE_ALL_EXCEPT) before calling these functions.  On return, if errno is  non-
       zero  or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero,
       an error has occurred.

RETURN VALUE
       Upon successful completion, these functions shall return the value of the error function.

       If x is NaN, a NaN shall be returned.

       If x is +-0, +-0 shall be returned.

       If x is +-Inf, +-1 shall be returned.

       If x is subnormal, a range error may occur, and 2 * x/ sqrt(pi) should be returned.

ERRORS
       These functions may fail if:

       Range Error
	      The result underflows.

       If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be
       set  to	[ERANGE].  If  the integer expression (math_errhandling & MATH_ERREXCEPT) is non-
       zero, then the underflow floating-point exception shall be raised.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       Underflow occurs when |x| < DBL_MIN * ( sqrt(pi)/2).

       On  error,  the	expressions  (math_errhandling	&  MATH_ERRNO)	and  (math_errhandling	&
       MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       erfc()  ,  feclearexcept()  ,  fetestexcept()  ,  isnan() , the Base Definitions volume of
       IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for  Mathematical  Func-
       tions, <math.h>

COPYRIGHT
       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable	Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
       the Institute of Electrical and Electronics Engineers, Inc and  The  Open  Group.  In  the
       event  of  any  discrepancy  between this version and the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					   ERF(P)
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